The present invention relates generally to angular position sensor, and more particularly to an angular position sensor that includes a rotatable magnet and a magnetically sensitive device to measure the angular position of a throttle plate.
The angular position of a rotatable member is a parameter of interest in numerous applications. In particular, angular position sensors are necessary to determine the angle of a throttle plate in an internal combustion engine. The angle of the throttle plate determines the amount of fresh air that is being utilized in the combustion process, and thus partially determines the power output of the engine. Because slight angular deviations in the throttle plate angle are important for systematic engine control, it is imperative that the angular position sensor have very high tolerance.
Suitable angular position sensors have historically used a rotatable magnet that is electromagnetically coupled to a sensing device, such as a Hall effect sensor. However, in certain configurations, the readings of the sensing device may have been compromised. A Hall effect sensor, for example, operates by generating an electrical current in response to a transverse magnetic field, such as the one caused by the rotatable magnet. As the magnitude of any magnetic field obeys the inverse-square law, any slight alternation of the distance between the Hall sensor and the field generating member would compromise the angular position reading.
In response to the foregoing concerns, one sensor provided a pair of pole pieces for transmitting the magnetic field of the rotatable magnet to the Hall effect sensor, which was preferably located a distance from the rotatable magnet. The pole pieces were symmetrical about an axis sharing the rotatable magnet and the Hall effect sensor, and further described as substantially L-shaped or substantially C-shaped. The Hall effect sensor was preferably placed at the narrow gap at the bottom of the L-pairing or C-pairing such that the transmitted magnetic field passed perpendicularly through the Hall effect sensor.
Although the angular position sensor contemplated by the foregoing sensor solves a number of prior limitations, it does not completely eradicate the technical obstacles of angular position sensing. For example, a typical angular position sensor will use multiple Hall effect sensors to ensure the accuracy of the measurements, due in large part to the potential errors in spatial variation of the magnetic field. Nevertheless, the above system focuses the magnetic field to a narrow gap, through which the magnetic field will vary greatly. Because the area of the surfaces projecting the magnetic field is small relative to the size of the sensing mechanism, the sensing mechanism is subject to increased gradient changes in the magnetic field. Consequently, if multiple Hall effect sensors have different measurements, it is not possible to settle the discrepancy based upon spatial variation of the sensors alonexe2x80x94it is also possible that the magnetic field is not sufficiently uniform to ensure accurate readings.
Moreover, as noted previously, a common application of angular position sensors is as part of a control system of an internal combustion engine. A side effect of locating the angular position sensor in such an environment is the presence of unwanted and unaccountable electromagnetic fields. Electrical current, rotors, and stators are all moving within the vehicle engine compartment, and they are all emanating magnetic fields in the direction of the angular position sensor. The foregoing sensor permits electromagnetic fields to enter the measurement apparatus through the end opposite to the Hall effect sensors. Due to the sensitivity of the sensors, any electromagnetic interference from external devices compromises the accuracy of the angular measurements.
Accordingly, the present invention provides an angular position sensor that uniformly focuses a magnetic field to a plurality of sensing devices while preserving the purity of that field. In particular, the present invention is an angular position sensor including a rotatable magnet disposed for rotation about a first axis and generating a variable magnetic field in response to rotation about the first axis. Also included is at least one magnetically sensitive device disposed remotely from the rotatable magnet along a second axis, where the second axis is perpendicular to the first axis. The at least one magnetically sensitive device is preferably a plurality of Hall effect sensors disposed on a circuit board for processing the generated electrical signals. The use of multiple Hall effect sensors is particularly applicable in providing redundancy to electronic vehicle control systems, such as throttle position regulation.
The focusing element of the angular position sensors includes six total segments. A first pole piece has a first segment, a second segment, and a third segment; and a second pole piece has a fourth segment, a fifth segment, and a sixth segment. The first segment and the fourth segment are disposed about the second axis at a first distance such that the first segment and the fourth segment are mutually parallel to the second axis. The third segment and the sixth segment are disposed about the second axis at a second distance such that the third segment and the sixth segment are mutually parallel to the second axis, the second distance being less than the first distance. The second segment and the fifth segment are disposed about the second axis such that the second segment and the fifth segment are at an angle to the second axis so that the pair of pole pieces converge on the second axis. Additionally, the angular position sensor of the present invention further includes a shielding member disposed about the first segment and the fourth segment for effectively shielding the angular position sensor from background magnetic fields. Alternatively, a second shielding member may be placed about the third segment and the sixth segment for preserving the uniformity of the magnetic field therebetween.